The purpose of this project is to evaluate methods for remediating the math deficits of students with two subtypes of math disability (MD) for whom the developmental course, as well as cognitive and neural correlates, are hypothesized to differ: those with comorbid math and reading disability (MD-RD) and those with MD alone. The signature feature of the MD-RD subtype is persistent difficulty in learning and retrieving math facts. For the second subtype, MD alone, the core deficit is chronic difficulty with procedural math (i.e., counting difficulties, reliance on erroneous algorithms to solve multi-digit computational problems, and faulty estimation). Both groups suffer concomitant problems with arithmetic story problems. Research on these MD subtypes has focused almost exclusively on performance differences. Little is known about (a) the potential to remediate the math deficits associated with these MD subtypes, (b) what the appropriate focus and nature of that intervention should be, (c) what transfer effects to math and reading might be expected with intervention, (d) the cognitive and neural correlates of responsiveness to intervention, (e) what role attention plays in intervention success, and (f) whether a-e vary as a function of MD subtype. To answer these questions, we identify students with two subtypes of MD: MD-RD and students with MD alone. Stratifying by MD subtype, we randomly assign students to treatments and examine responsiveness, as a function of MD subtype, on skill acquisition as well as transfer to other areas of math and to reading. We focus on short-term and longitudinal effects. In the first multi-year study (n = 320 across Years 2 and 3), we use this design to assess the potential to remediate the core deficits of fact retrieval and procedural skill. Students are randomly assigned to 4 treatments that systematically vary fact retrieval and procedural skill instruction: control (word identification), fact retrieval, procedural skill, or procedural skill plus fact retrieval. In the second multi-year study (n = 320 across Years 4 and 5), we use an analogous design to assess the potential to remediate arithmetic word problem deficits. Students are randomly assigned to 4 treatments that systematically vary arithmetic word problem instruction and fact retrieval instruction: control (word identification), arithmetic word problem strategies (i.e., cognitive strategies, schema induction, and diagrams), fact retrieval, or arithmetic word problem strategies plus fact retrieval. Project 1 (Cognition) relies on this intervention study conducted in Project 2 (Intervention) to examine cognitive and neural correlates of growth and to explore the role attention plays in determining responsiveness to treatment. Projects 3 (MRI) and 4 (MSI) rely on this intervention study to examine neural changes associated with treatment.